As a result of general sheridan’s use of the total war strategy during the shenandoah valley campaign, the south
retaliated by marching to the sea.
could not provide supplies for its army.
surrendered and brought an end to the war.
vowed to destroy civilian resources in the north.

The answer was the South could not provide supplies for its army. Sheridan applied a “scorched earth” campaign in the valley.  He had burned and destroyed anything that could be of use to the rebels.  Though General Jubal Early launched a surprise attack that caught the Union off guard, Sheridan rallied the men and turned the tables defeating Early and the Senandoah Valley was closed to the South.

less available tax revenue

this basically means that when they get money from taxes wirth having a lower gdp they get less then what others have with a higher gdp

i believe it would influence their own way of understanding things. it shall be a foundation where they can draw or start an argument.   historians are also  scientists that  have their tools of analysis and expertise to unlock a variety of difficulties such as relationships of man, origin, politics, economy, and culture. based on facts and understanding on these areas, they may shade light to extract ideas and develop options to validate a hypothesis or debunk it.